Alloy



Patented Aug. 4, 1936' UNITED STATES ALLOY Franz R. Hensel, Indianapolis, Ind., assignor, by mesne assignments, to P. B. Mallory 8t 00., Inc., Indianapolis, Ind., a corporation of Delaware No Drawing. Application February 23, 1935, Serial No. 7,841

6 Claim.

This invention relates to alloys and more particularly to copper base alloys of improved characteristics.

An object of the invention is to improve the casting qualities of copper base alloys of the type disclosed.

Another object is to provide an alloy of high hardness, coupled with improved electrical and thermal characteristics.

Further objects are to improve the crystalline characteristics of the alloy, including its grain size.

Other objects of the invention will be apparent from the following description taken in connection with the appended claims.

The present invention comprises the combination of elements, methods of manufacture, and the product thereof brought out and exemplified in the disclosure hereinafter set forth, the scope of the invention being indicated in the appended claims.

While a preferred embodiment of the invention is described herein, it is contemplated that considerable variation may be made in the method of procedure and the combination of elements without departing from the spirit of the invention.

The invention relates to alloys of copper, cadmium, chromium and silver. While these a1- loys may vary in their physical characteristics with the type of treatment received and the proportions of the various ingredients they will generally be characterized by high conductivity and hardness, heat resistanceand resistance to areing. These alloys may likewise be characterized by small grain size, and this characteristic may contribute to the other desirable properties.

It is contemplated that alloys may be produced, according to the invention, having the ingredients combined in the following range of proportions:

For most purposes, however, the most desirable characteristics may be attained if the proportions are kept within the following limits:

Per cent Cadmium 0.25 to 1.00 Silver 0.04 to 1.0 Chromium 0.4 to 0.8v Copper Remainder In carrying out the present invention a copper-cadmium-silver alloy may first be made according to the conventional alloy making procedure of the prior art and the chromium may then be added. For example, the copper-cad- 5 mium-silver alloy may be made by melting together the desired proportions of these metals and the chromium, in finely divided form, may then be introduced into the melt and intimately mixed therewith. The chromium is preferably 10 added, however, in the form of briquettes made by mixing together and compressing finely divided chromium and copper. These copper and chromium powders are commercially available and any .type of hydraulic press can be used for 15 I compressing. The addition of silver is made mainly to replace a proportionate part of the cadmium. This substitution results in better physical properties. An equal tensile strength may be obtained with a higher conductivity or 20 for the same conductivity 9. higher tensile strength may be obtained by replacing part of the cadmium by silver. The alloy can also be more easily handled in hot working operations. The temperatures need not to be in as narrow 5 a range as in the case of a straight copper-cad mium-chromium alloys of the same total alloying constituents.

The substitution of silver for cadmium has further a tendency to improve the stability of 30 the cold worked alloys at elevated temperatures.

The present alloy has greater fluidity in the molten state than alloys such as copper-chromium-silver without cadmium. This renders the alloy outstanding in its casting qualities, making it possible to successfully cast intricate designs and also resulting in castings of high density and freedom from flaws, open spaces or holes. There are indications that the silver likewise contributes to. the high casting qualities of the alloy.

In the further treatment of the alloy it may be first heated to a temperature of 600 C. to 1000 C. and preferably above 700 C. for a short time, such as from 10 to 30 minutes. After the metal has reached the desired temperature it may be cooled quickly from the high temperature (quenched).

By using the present alloy it is possible to use lower quenching temperatures and to obtain greater hardness in the quenched alloy than with ternary alloys, such as copper-chromium-silver. The hardness of these ternary alloys, on quenching, drops to a minus Rockwell B reading while 55 the present alloy will have a hardness in the quenched state of 10-15 Rockwell B.

For most purposes the next step is to heat treat the quenched alloy at a temperature of 350 C. to 600 C. for a period of from 10 minutes to 30 hours, depending on the temperature, the per-- centages of alloying ingredients used, and the results desired.

The alloy may then be cold worked to obtain a cold reduction of approximately 20% and further cold reduction, up to 50% or more, may be applied to further increase the hardness. It has been found that the conductivity will not be appreciably decreased by these further reductions.

For maximum hardness and conductivity, however, it is preferable to apply a series of cold reductions alternated with relatively low temperature heat treatments, preferably within the range 350 C. to 500 C. The number of cold workings with intermediate heat treatments may vary with the properties desired in the finished product. The present alloys are found to be more susceptible to hardening by cold working than such ternary alloys as mentioned above.

Instead of the cold working the alloys may be hot forged according to usual methods and it will be found that the resulting hot-forged product will also have a hardness greater than the alloys of the prior art previously mentioned.

The present alloy when cast and heat treated has been obtained at a hardness of 60-70 on the Rockwell B scale and a conductivity of approximately 75% to 85% that of copper. After heat treatment and a cold reduction of about 20% the hardness was increased to 80 Rockwell B.

The heat-resistant properties of the present alloy likewise greatly improved, the hardness and electrical conductivity being maintained indefinitely at temperatures in the order of 400 C. to 470 C.

The greater hardness and improved thermal characteristics are obtained without diminishing "the resistance of the alloy to electric arcing and, fact, with considerable improvement in are i resistance.

'= a total alloying content of approximately 1.25%

decreases the solid solubility of the chromium in copper making it possible to obtain high hardness with. much smaller proportion of chromium. The present alloys have been made, for example, containing below 0.35% chromium and having a hardness of 60-70 Rockwell B after complete heat treatment. It is thought that the decrease in solid solubility of copper and chromium, due to te combined presence of the cadmium f and silver is largely responsible for the higher electrical conductivity in the present alloy.

The combined addition of cadmium and silver eliminates certain disadvantages heretofore associated with such alloys as copper-chromium among which may be mentioned the tendency to grain growth when heated to high temperatures. This has brought about frequent fractures at the grain boundaries, rendering the castings unsuitable for many purposes and frequently causing failure during cold working or hot forging.

temperatures.

Another difllculty encountered with such cop per-chromium alloys as the above is the rapid surface oxidation at elevated temperatures. If a copper-chromium alloy is heated to a high temperature a soft shell is formed on the surface, un- 5 doubtedly due largely to the oxidation of the chromium. There is a strong indication that the oxygen penetrates into the body of material along the grain boundaries thereby causing an inter-crystalline weakness of-the heat-treated 1o material. The tendency of the alloy to form large grains at high temperatures favors this intercrystalline penetration of oxygen.

The combined addition of the cadmium and silver in the proportions indicated above is found to overcome a large part of the above difficulties. The grain size is kept markedly smaller. For example, with copper-chromium alloys, having these metals in substantially the proportions given above, it has been found that after heating the alloys to 975 C. for one hour the number of grains per square millimeter was 30 to 50. With the present alloys, containing cadmium and silver, however, the number of grains resulting after the same treatment is 400 to 500 per square milllmeter.

It will be readily recognized that the above grain refinement yields an enormous improvement in the qualities and characteristics of this type of alloy. By using silver alone this grain refinement could not be obtained. It is therefore combined presence of cadmium and silver which is responsible for it.

The presence of cadmium and silver alloyed with the copper and chromium is found to reduce the soft oxidized surface layer to about one-third that found on alloyssuch as copper-chromium without cadmium and silver. If the alloy con taining cadmium and silver is heated only five minutes at 975 C. no perceptible soft layer is formed at all. If a binary alloy of copper and chromium is given the same treatment, however, a soft layer is formed to a depth of almost onesixty-fourth inch.

On account of the low boiling point of the cadmium it tends to oxidize in preference to the other alloying ingredients particularly in preference to chromium. This preferential surface oxidation of cadmium protects the alloy at elevated It also gives the alloy high arc snufing qualities.

The present alloy is much less susceptible to intercrystalline cracking than the above mentioned copper-chromium alloys. There is a enclency in copper-chromium base alloys to embrittlement in the temperature range where aging takes place. Oxide films along the grainboundaries and large grain size both contribute to this cracking. The presence of the cadmium and silver in the present alloy appears to be large- 1y responsible for the reduction in cracking.

This alloy is exceptionally well adapted, because of the above properties, to the production of castings, such as cylinder heads and pistons, and of resistance welding electrodes, commutator segments, collector rings, trolleys, trolley wheels, trolley shoes, contacts, contactors, and the like. For each application the materials may be used in such proportions as to obtain the desired hardness and conductivity. 0 While the present invention, as to its objects and advantages, has been described herein as carried out in specific embodiments thereof, it is not desired to be limited thereby but it lslntended to cover the invention broadly within the spirit and scope of the appended claims.

What is claimed is:

1. An alloy containing about 0.1% to 1.5% chromium, 0.03% to 1.0% silver, 0.1% to 1.25% cadmium and the remainder copper.

2. An alloy consisting of 0.4% to 0.8% chromium, 0.04% to 1.0% silver, 0.25% to 1.0% cadmium and the remainder copper.

3. An alloy containing about 0.1% to 1.5% chromium,. 0.03% to 1.0% silver, 0.1% to 1.25% cadmium and the remainder substantially all copper, characterized by greater fluidity in the molten state than alloys of copper, chromium and silver, high resistance to oxidation, such that no perceptible soft layer is formed on the surface of the alloy when it is heated to 975 C. for five -minutes, a resistance to grain growth sufllcient to keep the grain count in the order of 400 to 500grains per square millimeter after heating for one hour at 975 C., and a quenched hardness in the order of 10 to 15 Rockwell B.

4. An age hardened alloy containing about 0.1% to 1.5% chromium, 0.03% to 1.0% silver 0.1% to 1.25% cadmium and the remainder substantially all copper, characterized by a hardness in the order of to 80 Rockwell B, electrical conductivity in the order of to 85% of that of copper and the ability to retain its hardness and electrical conductivity indefinitely at temperatures in the order of 400 C.

5. An electrode suitable for use in resistance welding devices, electric oontactors and the like containing about 0.1% to 1.5% chromium, 0.03% to 1.0% silver, 0.1% to 1.25% cadmium and the remainder copper.

6. An electrode suitable for use in resistance welding devices, electric contactors and the like containing about 0.1% to 1.5% chromium, 0.03% to 1.0% silver, 0.1% to 1.25% cadmium and the remainder substantially all copper, characterized by a hardness in the order of 60 to Rockwell B, electrical conductivity in the order of 75% to ct that of copper and the ability to retain its hardness and electrical conductivity indefinitely at temperatures in the order of 400 -C.

FRANZR.HENSEL. 

